Exemplary high power, cw, electrically excited flowing gas lasers are disclosed in U.S. Pat. No. 3,962,656 to E. R. Peressini and in U.S. Pat. No. 3,970,962 to E. R. Peressini et al, both patents being assigned to the assignee of the present invention. In lasers of this type, the laser gas flows through an excitation region where it is excited to a condition of population inversion by an electric discharge controlled by an electron beam introduced into the excitation region from an adjacent electron gun. The discharge is established between an anode and a cathode disposed on opposite sides of the gas flow channel at the excitation region. The electrons in the electron beam and in the discharge current travel in a direction transverse to the glas flow direction.
It is sometimes desirable to operate lasers of the foregoing type at laser gas pressures approaching or even exceeding atmospheric pressure in the excitation region. When operating at such pressures, as the power level is increased it becomes more difficult to maintain a uniform, homogeneous discharge in the region adjacent to the cathode. Eventually, a limit is imposed on the power level at which the laser may be reliably operated.
In high pressure chemical lasers utilizing an electric discharge transverse to a flowing gas mixture, the stability and uniformity of the discharge have been improved by introducing a pair of auxiliary gas streams into the flowing gas mixture upstream from the discharge region and by causing these streams to flow through the discharge region immediately adjacent to the respective discharge electrodes. Ionization in the auxiliary gas streams produces a sufficient number of electrons to effectively provide "plasma electrodes" adjacent to the actual discharge electrodes. These plasma electrodes reduce the electric field near the electrode surfaces. A specific exemplary chemical laser which employs auxiliary gas streams (consisting of a mixture of He and SF.sub.6) in the aforedescribed manner is disclosed in the Final Technical Report--Phase I under Contract DAAH01-75-C-0412 entitled "High Pressure CW Chemical Laser," by David Wrench, Hughes Research Laboratories, November 1976, particularly at pages 22, 29, 32 and 33.
When employing an auxiliary gas stream arrangement of the aforedescribed type, great care must be taken to properly match the velocities of the auxiliary and the laser gas streams or excessive mixing of the auxiliary and the laser gases will occur. Moreover, even with optimum velocity matching, sufficient gas mixing occurs so that the effectiveness of the auxiliary gas streams is reduced in the downstream region of the discharge.